In the production process of the luggage and garment industry, it is very important to choose the quality and specifications of the sewing thread. The sewing thread is used to sew various garment fabrics and other auxiliary materials, and has the dual functions of practicality and decoration. The quality of the stitching not only affects the sewing effect and processing cost, but also affects the appearance quality of the finished product. People engaged in the clothing industry must understand the general concept of stitch formation, twist, the relationship between twist and strength, stitch classification, characteristics and main uses, and the selection of stitches. The following is a brief introduction! 1. The concept of line Carding (carding) refers to a yarn that is spun by carding only one end. Combing refers to the yarn combed at both ends of the fiber with a combing machine, the impurities have been removed, and the fiber is straighter. Blending refers to yarns in which two or more fibers of different properties are mixed together. Single yarn refers to the yarn formed directly on the spinning frame, and it will disperse once it is untwisted, and it is called yarn for short. Strand yarn refers to two or more yarns twisted together, referred to as thread. Sewing thread refers to the general name of the thread used for sewing garments and other sewing products. ... The new type of spinning is different from traditional ring spinning in that one end is a free end, such as open-end spinning and friction spinning. The yarns are tangled together and have no twist. Yarn count is an index used to indicate yarn fineness, mainly including English count, metric count, special count, and denier. 2. About twist Concept: Twist the fiber structure of the thread to produce a relative angular displacement between the cross-sections of the thread, and change the structure of the thread by tilting the straight fiber and the axis. Twisting can make the yarn have certain physical and mechanical properties such as strength, elasticity, elongation, luster, hand feeling, etc. It is expressed by the number of twists per unit length, commonly used twists per inch (TPI) or twists per meter (TPM) . Twisting: rotating 360 degrees around the axis is a twisting. Twisting direction (S direction or Z direction): When the yarn is vertical, the inclination direction of the spiral formed by rotating around the axis. The inclination of the S twist direction is the same as the middle of the letter S, that is, the right-hand direction or the clockwise direction. The inclination of the Z twist direction is consistent with the middle of the letter Z, that is, the left-hand direction or the counterclockwise direction. The relationship between twist and strength: the twist of the thread is proportional to the strength, but after a certain twist, the strength decreases. If the twist is too large, the twist angle will increase, and the thread will have poor luster and hand feel; if the twist is too small, hairiness will occur and the hand will feel loose. This is because the twist increases and the frictional resistance between the fibers increases, which increases the strength of the thread. However, as the twist increases, the axial component of the yarn becomes smaller, and the stress distribution of the inner and outer fibers is uneven, resulting in inconsistent fiber breakage. In short, the breaking performance and strength of the thread are closely related to the twist. The twist and the twist direction are determined according to the needs of the finished product and post-processing, generally the Z twist direction.